Not my idea, wasn't representing it as my idea; djb proposed it long ago (as other commenters in this thread mentioned), and as you pointed out as IPv4 mapped addresses. I was just describing how it might work, since it's a little confusing. In particular when I first started thinking about it I kept getting stuck on "Ok, so how do non-v4 mapped IPs talk to v4 addresses?"

> Not my idea, wasn't representing it as my idea; djb proposed it long ago (as other commenters in this thread mentioned), and as you pointed out as IPv4 mapped addresses. I was just describing how it might work, since it's a little confusing.

Every time IPv6 comes up some number of people talk about a protocol that 'just' added more bits IPv4 and calling it a day. But when going over the details of how what would work, exactly, you end up at the same place as IPv6 (and various 'transition mechanisms').

But there is no 'just' adding more addresses: you need to update (at least) end-hosts, update DNS, have relays/proxies if the middle of your network does not support IPng, have tunnelling to/from those special translation systems. It's basically the same thing as IPv6.

Certainly you can argue about keeping ARP versus going with NDP. Or not having SLAAC—but then you need infrastructure like DHCP (which is optional with IPv6).